Assessment Comments

Assessment is based on: (1) IDNR/UHL monthly ambient monitoring conducted during the 2008-2010 assessment period at the County Road F-58 bridge NE of Missouri Valley (STORET station 10430001 (formerly station 822304)) and (2) USGS chemical/physical water quality monitoring at Logan, IA, from February 2008 through December 2010.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW1) aquatic life uses, including fish consumption uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf) and due to the results of an Use Attainability Analysis in 2006, this segment is also now designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of chemical/physical water quality monitoring conducted from 2008 through 2010.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.   This assessment is based on results of (1) IDNR/UHL monthly ambient monitoring conducted during the 2008-2010 assessment period at the County Road F-58 bridge NE of Missouri Valley (STORET station 10430001 (formerly station 822304)) and (2) USGS chemical/physical water quality monitoring at Logan, IA, from February 2008 through December 2010.  

EXPLANATION:  The Class A1 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.   The geometric means of indicator bacteria (E.  coli) in the 14 samples collected during the recreational seasons of 2009 through 2010 at the Boyer River at Logan by USGS were as follows: the 2009 geometric mean was 4865 orgs/100 ml and the 2010 geometric mean was 2835 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Thirteen of the 14 samples (93%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”  

The geometric means of indicator bacteria (E.  coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at the Boyer River near Missouri Valley through the IDNR/UHL ambient stream monitoring program were as follows: the 2008 geometric mean was 1965 orgs/100 ml, the 2009 geometric mean was 841 orgs/100ml, and the 2010 geometric mean was 759 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Sixteen of the 21 samples (76%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”  

Regarding support of the Class B(WW1) aquatic life uses, monitoring at the IDNR/UHL station NE of Missouri Valley showed no violations of Class B(WW1) water quality criteria for pH (range = 7.6 to 8.5), dissolved oxygen (minimum = 6.8 mg/L), or ammonia (maximum = 1.7 mg/L) in the approximately 32 samples analyzed during the 2008-2010 period.  These results suggest "full support" of the Class B(LW) uses in this segment of the Boyer River.      

The results of USGS monitoring near Logan, IA, showed no violations of Class B(WW1) criteria for dissolved oxygen (minimum = 6.5 mg/L), pH (range = 7.4 to 8.8) or ammonia (maximum = 0.9 mg/L) in the 30 samples collected or for the pesticides dieldrin and DDE in the 30 samples collected.   There was, however, one violation of the Class B(WW1) criterion for chlorpyrifos in 30 samples.   Based on IDNR's assessment methodology more than one violation of a chronic water quality criterion for a toxic pollutant in an abundant data set indicates an impairment of aquatic life uses.   Therefore, the single violation of the chronic chlorpyrifos water quality criterion in 30 samples does not suggest an impairment of the Class B(WW1) aquatic life uses.   Thus, the results from both the IDNR and USGS monitoring stations suggest "full support" of the Class B(WW1) aquatic life uses.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.